1. Field of the Invention
The present invention relates to glazings with variable optical/energetic properties. It relates more precisely to glazings whose characteristics can be modified, for example, under the effect of an electrical supply, for example, light diffusion or the transmission within some wavelengths of the electromagnetic spectrum, especially in the infrared and/or in the visible, or under the effect of a particular radiation.
2. Discussion of the Background
An increasingly growing demand exists for so-called "intelligent" glazings, or glazings whose properties can be modulated at will, in order to take various changing parameters into account. It is highly advantageous to be able to control the input of sunlight through glazings fitted externally in buildings, motor vehicles, or trains, in order to avoid excessive heating of the rooms or compartments in the event of strong sunshine. Similarly, it may be useful to control the degree of vision through glazings, for example in the case of glazings employed as internal partitions between two rooms, in a building, or between two compartments in a train or an aircraft. Many other applications also exist for such glazings: for example, rearview mirrors in vehicles which, by becoming darker when required, can prevent dazzling of the driver, or road or urban sign panels displaying mileages or designs only intermittently in order to attract attention better.
The interest in such glazings accounts for the fact that many such systems have already been studied.
One of the known systems that make it possible to modulate the light transmission or absorption of glazings are especially the so-called viologen systems like those described in U.S. Pat. No. 5,239,406 or in Patent EP-A-0 612 826. The latter makes it possible to obtain a variable absorption essentially in the visible range.
For the same purpose there are also the so-called electrochromic systems, which include a layer of an electrochromic material capable of reversibly and simultaneously inserting cations and electrons, and whose oxidation states corresponding to the inserted and disinserted states have different colors, one of the states exhibiting a higher light transmission than the other. The insertion or disinsertion reaction in driven by a suitable electric supply with the aid of a current generator or a voltage generator. The electrochromic material, usually tungsten oxide-based, is placed in contact with a source of electrons, such as a transparent electrically conductive layer, and a source of cations, such as an ionically conductive electrolyte.
To ensure at least about a hundred switchings, the layer of electrochromic material must be combined with a counterelectrode, itself also capable of reversibly inserting cations, symmetrically in relation to the layer of electro-chromic material, so that, macroscopically, the electrolyte appears to be a simple medium for the cations.
The counterelectrode must consist of a layer which is either neutral in color, transparent, or weakly colored when the electrochromic layer is in the faded state. Since tungsten oxide is a cathodic electrochromic material, that is to say its colored state corresponds to the most reduced state, an anodic electrochromic material such as nickel oxide or iridium oxide is generally employed for the counterelectrode. It has also been proposed to employ a material which is optically neutral in the oxidation states involved, such as, for example, curium oxide, or organic materials like electronically conductive polymers (polyaniline, etc.) or Prussian blue.
The description of such systems will be found, for example, in European Patents EP-0 338 876, EP-0 408 427, EP-0 575 207 and EP-0 628 849.
At present these systems can be classified into two categories, according to the electrolyte type employed:
1. either the electrolyte is in the form of a polymer or of a gel, for example a proton-conducting polymer like those described in European Patents EP-0 253 713 and EP-0 670 346 or a polymer conducting lithium ions, such as those described in Patents EP-0 382 623, EP-0 518 754 and EP-0 532 408; or PA1 2. the electrolyte is an inorganic layer, ionically conductive but electronically insulating; "all-solid" electrochromic systems is the term which is then employed. For the description of an "all-solid" electrochromic system reference may be made to French Patent Application FR-96/03799 filed on Mar. 27, 1996. PA1 at least one active layer, and PA1 at least one reflecting coating on said active layer. PA1 a glazing, containing at least one active layer and at least one reflecting coating. PA1 coating at least one reflecting coating onto the surface of an active layer. PA1 on the one hand, the invention makes it possible to lengthen the lifetime of the "intelligent" glazings which were already intended for external applications. This is commercially and technically highly advantageous, both in the field of building construction, where the builders must guarantee lifetimes of the materials employed of at least 5 or 10 years, and in the motor vehicle sector, where strict safety standards apply, especially in terms of optical quality; PA1 on the other hand, the invention makes it possible to envisage "intelligent" glazings for external applications, hitherto employed essentially internally for reasons of excessively poor thermal durability, and/or of instability towards certain radiations, which is, for example, the case with some liquid-crystal glazings employing dichroic dyes which are relatively unstable to ultraviolet radiations. PA1 dielectric/silver/dielectric or PA1 dielectric/silver/dielectric/silver/dielectric, optionally with, between the silver layer and at least one of the adjacent layers of dielectric, thin layers based on partially or completely oxidized metal, intended to act as nucleation layers and/or barrier layers, especially against oxidation. PA1 glass 1/reflecting coating/sheet of bonding polymer/glass 2/electrochromic system/glass 3. This reflecting coating may alternatively be placed on the face of the glass 2 facing the sheet of bonding polymer or on the external face of the glass 1 if it has sufficient mechanical and chemical durability. This laminated structure may be fitted as insulating double glazing, then, for example, with the sequence glass 1/reflecting coating/sheet of bonding polymer/glass 2/electrochromic system/glass 3/gas interlayer/glass 4. PA1 glass (1) /reflecting coating/sheet of bonding polymer/sheet of flexible polymer/liquid-crystal system/sheet of flexible polymer/sheet of bonding polymer/glass (2). As in the case of the electrochromic glazing, the reflecting coating may alternatively be situated especially on the external face of the glass 1. PA1 glass 1/reflecting coating/gas interlayer/electrically controllable system used in combination with at least one glass 2. PA1 clear glass 1/reflecting coating/ . . . /electrically controllable system of the liquid-crystal type/ . . . /tinted glass 3, the dots representing at least one material of the rigid substrate, sheet of bonding polymer or gas interlayer type. PA1 when the electrically controllable system has variable absorption, as is the case with an electrochromic system, it is, in fact, liable to be heated by strong sunshine via an energy absorption phenomenon when it is in the colored state, and hence the advantage of the reflecting coating according to the invention (the same comment applies to the photochromes); and/or PA1 when the electrically controllable system is of the liquid-crystal type or when it is a system with variable absorption of the electrochromic type which is in the faded state, it is better to avoid it being in contact with a tinted glass subjected directly to sunshine, to avoid its becoming heated by this contact, even if it is not absorbent itself.
These systems containing reversible-insertion material(s) are particularly advantageous in the sense that they allow the absorption to be modulated in a wider range of wavelengths than the viologen systems; they can absorb in a variable manner not only in the visible but also in the infrared, and this enables them to assume an efficacious optical and/or thermal function.
The viologenic or electrochromic systems deposited or combined with transparent substrates form glazings whose light absorption and transmission (as well as the energy transmission) can vary within given ranges. The ranges are typically determined by the choice of the electrochromic materials employed and/or their thickness.
Another type of "intelligent" glazing includes what is referred to by the term of optical valve: this is a film including a matrix of generally crosslinked polymer(s) in which are dispersed microdroplets containing particles which can orient in a preferred direction under the action of an electric or magnetic field.
The above film exhibits variable optical properties as a function of the electrical potential applied to the terminals of the conductive layers placed on both sides of the film and of the concentration and the nature of the orientable particles.
Thus, Patent WO-93/09460 discloses an optical valve based on a film including a matrix made of crosslinkable polyorganosilane and inorganic or organic orientable particles, more particularly light-absorbing particles such as polyiodide particles. When a voltage is applied to the film, the particles intercept the light much less than when there is no voltage.
A glazing which operates on a similar principle is also known under the term of liquid-crystal glazing. It is based on the use of a film placed between two conductive layers and based on a polymeric material in which are dispersed droplets of liquid crystals, especially nematic with positive dielectric anisotropy. When a voltage is applied to the film the liquid crystals orient themselves along a preferred axis, and this permits vision. With no voltage, in the absence of alignment of the crystals, the film becomes diffusing and prevents vision.
Examples of such films are described in European Patent EP-0 238 164 and U.S. Pat. No. 4,435,047, U.S. Pat. No. 4,806,922 and U.S. Pat. No. 4,732,456. Films of this type, once laminated and incorporated between two glass substrates, are marketed by Saint-Gobain Vitrage under the trade name "Priva-lite".
All the liquid-crystal devices known under the terms of "NCAP" (Nematic Curvilinearly Aligned Phases) or "PDLC" (Polymer Dispersed Liquid Crystal) can in fact be employed.
It is also possible to employ, for example, gels based on cholesteric liquid crystals containing a small quantity of crosslinked polymer, like those described in Patent WO-92/19695.
So-called photochromic glazings also exist in which the property of absorption in the visible and possibly in at least a portion of the infrared can be modulated under the effect of energetic radiation, generally situated in the ultraviolet. There are mainly two classes of these; the first employs silver salts, especially silver halides, as the active components, for example, in a glassy matrix, halides which by absorption in the ultraviolet are converted reversibly into a form of metal aggregates. The second class employs as the active components organic dyes that are generally dispersed in a polymer matrix, especially compounds derived from spiroxazines and spiropyrans. These compounds are isomerized reversibly by absorption in the ultraviolet.
However, all of the above glazings exhibit intrinsic limits with respect to their thermal behavior and to their optical appearance.
In fact, these glazings, mentioned above, include a plurality of electrically and/or electrochemically active components whose durability can depend on the temperature to which they are subjected. In the particular case of the glazings with variable light transmission, such as electrochromic glazings, when they are in the colored state they are highly absorbent with regard to energy. Thus, when they are employed as external glazings, and even more so if they are fitted inclined in relation to the vertical (which is the case with motor vehicle glazings such as car roofs or glazings for building roofing), they can, in the colored state, heat up to high temperatures reaching 80.degree. C. when exposed for long enough to strong sunshine. Such temperatures can cause a shortening of the lifetime of the glazings by progressive irreversible degradation of one or other of their electrochemical components.
The same type of problem can also arise in the case of glazings with variable light diffusion, like liquid-crystal glazings. Firstly, beyond a certain temperature, called the clearing point, the liquid-crystal polymer composite, converted to a diffusing state, can spontaneously revert to the transparent state. Subsequently, if a dichroic dye has been added to the composite in order to make it possible to modulate both the light diffusion and a transmission of the glazing, this type of dye exhibits some degree of instability in the ultraviolet region, an instability that increases with temperature.
Photochromic glazings also have a disadvantage linked with their heating. In fact, the two classes of photochromic glazings referred to above become tinted under the effect of ultraviolet light: an "unstable" state. The return to the faded, "stable" state is obtained by a process which is heat activated. Under the effect of ultraviolet light these glazings take on color, become absorbent and therefore heat up. In strong sunshine the heating becomes excessive and tends to make the glazings revert to their faded stable state, and the "available" contrast decreases.
Furthermore, the optical appearance of the above glazings may not be fully satisfactory, depending on the intended applications. Thus, when a whole facade of a building is fitted with electrochromic glazing, it gives an overall appearance which is somewhat somber when all of it is in the colored state. It could also be advantageous to adjust the reflection appearance of an electrochromic glazing on a car according to the color of the external bodywork. Similarly, in the diffusing state, glazings containing liquid crystals offer a milky white appearance (in the absence of dye) which is identical regardless of the side on which a viewer is placed. Thus, it could be advantageous to be able to do away with this symmetry of appearance for aesthetic reasons.
Thus, there is a need for new glazings with variable optical and/or energetic properties that overcome these disadvantages and are capable of being controlled electrically or photochromically, which exhibit a greater thermal durability and/or whose optical appearance can be modulated to a greater extent.